Overview Of Singleton Pattern

Singleton Pattern is one of the software design patterns which uses only one instantiation of a class.

What is a Singleton Pattern?

Singleton Pattern is one of the software design patterns which uses only one instantiation of a class.

When do we use a Singleton Pattern?

When you want a single instance of a class to be active throughout the application lifetime.

Example - Error Logger

When values on one screen need to be utilized on another screen without the usage of Session concept. Example - Logged User Details

Difference between Static Class and Singleton Pattern

Static Class	Singleton Pattern
Cannot be instantiated.	Only one instance throughout the cycle.
Can contain only static members & static methods.	Can contain both static and non-static variables and methods.
Cannot have a simple public constructor.	Can have a simple public constructor.

Implementation

Add a static implementation of the same class datatype as one of the fields/properties.

public class Singleton
    {
        private static Singleton instance;

        private Singleton() { }

        public static Singleton Instance
        {
            get
            {
                if (instance == null)
                    instance = new Singleton();
                return instance;
            }
        }

        //instance methods
    }

Exception Logger

When you want to log the exception, you don’t need to instantiate every time you want to log. A single object can be used to log the exceptions. Below is a sample implementation of Exception Logging Service.

Code Snippet

using System;

public class ExceptionLoggingService
{
    private static ExceptionLoggingService _instance = null;

    public static ExceptionLoggingService Instance
    {
        get
        {
            if (Instance == null)
            {
                _instance = new ExceptionLoggingService();
            }
            return _instance;
        }
    }

    public void LogError(Exception ex)
    {
        try
        {

        }
        catch (Exception exx)
        {

        }
    }
}